The invention relates to a process for producing gamma-butyrolactone by catalytic hydrogenation of maleic anhydride in the vapor phase.
Gamma-butyrolactone is an important chemical, significant as a starting substance for numerous syntheses. It plays a role, for example, in producing butyric acid and its derivatives, butanediol, tetrahydrofurane, N-methylpyrrolidone, polyvinylpyrrolidone, methionine, and the like. Furthermore, gamma-butyrolactone is an important solvent for acrylates and polymers with a styrene basis, among others. It can also be used as a solvent in producing synthetic fibers, for example.
A number of production processes start from maleic anhydride or derivatives such as maleic acid, succinic anhydride, or maleic ester, which are subjected to hydrogenation. The hydrogenation is usually conducted in the vapor phase and in the presence of catalysts. The patent literature describes numerous catalysts for these reactions. For example, in U.S. Pat. No. 3,065,243, a process is disclosed in which copper chromite serves as a catalyst. From the description and the examples in this patent, this conversion also produces considerable amounts of succinic anhydride, which must be recirculated.
There has been no lack of attempts to develop catalysts to improve yield and selectivity. Another aim of the studies was to extend the useful life of the catalysts, since for many catalysts the useful life is too short for continuous operation; in continuous operation, the deactivation of the catalyst, usually by coking of the catalyst, is too rapid.
In Canadian Patent 840,452, enhanced catalysts are described which have copper/zinc as a basis. These can be processed together with asbestos to form corresponding catalyst particles. The catalyst claimed in this Canadian patent, as well as the copper chromite/asbestos catalyst produced in similar fashion, do not fulfill all requirements imposed on a good catalyst for the production of gamma-butyrolactone.
In the published application DE 24 04 493, a process is described in which hydrogenation is carried out in the presence of water vapor. This is intended to reduce coking of the catalyst. One of the disadvantages of this process is that water is not an inert compound, i.e., it is a reaction component and, thus, part of the equilibrium.
Other catalysts of copper chromite basis are described in U.S. Pat. No. 4,006,165, for example, wherein this catalyst must also contain nickel. These catalysts can either be deposited on aluminum oxide or silicas such as kieselguhr, or produced by mixing with these substances.
Although numerous catalysts have been described for conversion of hydrogen and maleic anhydride to gamma-butyrolactone, there is still the need for catalysts with which this conversion can be carried out in an improved and more advantageous manner.